Chapter 6 Questions

Question 1

What is the advantage of binocular summation?

Answer 1

The advantage of binocular summation is that detecting a stimulus can be done with two eyes, as opposed to just one, and so this yields more information about the stimulus.

Question 2

Explain the difference between a monocular depth cue and a binocular depth cue.

Answer 2

A monocular depth cue is available when the world is viewed with only one eye. A binocular depth cue requires information from both eyes.

Question 3

What is the idea behind positivism?

Answer 3

Positivism is a philosophical position arguing that all you really have to go on is the evidence of your senses, so the world might be nothing more than an elaborate hallucination.

Question 4

Name three monocular depth cues.

Answer 4

Any three of the following: occlusion, relative size, familiar size, relative height, texture gradients, linear perspective, aerial perspective, motion parallax, accommodation, or convergence.

Question 5

Explain what a texture gradient is.

Answer 5

A texture gradient is a depth cue based on the geometric fact that items of the same size form smaller images when they are farther away. Thus, an array of items that change in size across the image will appear to form a surface in depth.

Question 6

What kind of information does aerial perspective provide about the stimulus?

Answer 6

Aerial perspective is a depth cue that is based on the implicit understanding that light is scattered by the atmosphere. More light is scattered when you look through more atmosphere. Thus, more distant objects are subject to more scatter and appear fainter, bluer, and less distinct. Aerial perspective provides information about the relative distance of objects from the observer

Question 7

What is a vanishing point?

Answer 7

A vanishing point is the apparent point at which parallel lines receding in depth converge.

Question 8

What kind of movement does motion parallax depend on? Explain.

Answer 8

Motion parallax depends on either object movement or head movement. During either type of motion situation, closer objects move faster across the visual field than farther objects, allowing one to determine the depth of objects relative to each other.

Question 9

What is a pictorial depth cue?

Answer 9

A pictorial depth cue is a cue to distance or depth used by artists to depict three-dimensional depth in two-dimensional pictures.

Question 10

How are convergence and divergence important to depth perception?

Answer 10

Convergence and divergence are important to depth perception because they are used to place the two images of a feature in the world on corresponding locations in the two retinal images (typically on the fovea of each eye). They both reduce the disparity of that feature to zero, or nearly zero.

Question 11

Explain the concept of corresponding retinal points.

Answer 11

Corresponding retinal points are points on the retina of each eye where the monocular retinal images of a single object are formed at the same distance from the fovea in each eye. The two foveas are also corresponding points.

Question 12

Explain the concept of the Vieth-Müller circle, and how it relates to the horopter.

Answer 12

The Vieth-Müller circle refers to the location of objects whose images fall on geometrically corresponding points in the two retinas. If the two eyes are looking at one spot, then there will be a surface of zero disparity running through that spot (known as the horopter).

Question 13

What is the difference between crossed disparity and uncrossed disparity?

Answer 13

Crossed disparity is the sign of disparity created by objects in front of the plane of fixation (the horopter). Images of objects that are located in front of the horopter will appear to be displaced to the left in the right eye, and to the right in the left eye. Uncrossed disparity is the sign of disparity created by objects behind the plane of fixation. Images of objects that are located behind the horopter will appear to be displaced to the right in the right eye, and to the left in the left eye.

Question 14

What is a stereoscope?

Answer 14

A stereoscope is a device for presenting one image to one eye and another image to the other eye. Once these two images are fused by the observer, they create a single three-dimensional image with a strong impression of depth.

Question 15

When is free fusion used?

Answer 15

Free fusion is a technique of converging or diverging the eyes in order to view a stereogram without a stereoscope.

Question 16

What does stereoblindness often result from?

Answer 16

Stereoblindness, or the inability to make use of binocular disparity as a depth cue often results from a childhood visual disorder such as a strabismus, in which the two eyes are misaligned.

Question 17

What is a random dot stereogram?

Answer 17

A random dot stereogram is a stereogram made of a large number of randomly placed dots. The random dot stereogram contains no monocular cues to depth.

Question 18

When does one view cyclopean stimuli?

Answer 18

One views cyclopean stimuli when looking at random dot stereograms. These are stimuli that are defined by binocular disparity alone.

Question 19

Define the correspondence problem.

Answer 19

The correspondence problem is the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye.

Question 20

Name two ways of solving the correspondence problem.

Answer 20

Any two of the following: 1) Blurring the image to remove high spatial frequencies, so that there are not as many dots to analyze and 2) using the uniqueness constraint, in which a feature in the world will be represented exactly once in each retinal image, or 3) using the continuity constraint which assumes that neighboring points in the world lie at similar distances from the viewer, except at the edges of objects.

Question 21

In what sense does the Bayesian approach take into account past experience? Explain.

Answer 21

The Bayesian approach is a statistical model which states that prior knowledge could influence one’s estimates of the probability of a current event. In the case of vision, since the retinal images formed on the two retinas could be a result of an infinite number of scenes, this approach helps to narrow down the possible choices to the ones that are the most likely, based on past experiences.